Personality disorder get a bad press. To many people, it conjures up images of violence and fear, but doctors are undecided about who has a disorder, let alone how to treat it.

The term personality disorder covers a wide range of illness, including obsessive compulsive disorder and paranoia.

Doctors estimate up to 13% of the population may be suffering from a personality disorder.

The Royal College of Psychiatrists says current classifications are "deficient".

Definitions

The World Health Organisation (WHO) and the American Psychiatric Association (APA), two major international bodies on psychiatric health, agree on the general definition of personality disorder, although they each give different categories within the definition.

Severe or anti-social personality disorder is one of the most complex and controversial areas of classification.

The WHO defines personality disorder as: "Deeply ingrained and enduring behaviour patterns, manifesting themselves as inflexible responses to a broad range of personal and social situations.

"They represent either extreme or significant deviations from the way the average individual or a given culture perceives, thinks, feels and particularly relates to others.

"Such behaviour patterns tend to be stable and to encompass multiple domains of behaviour and psychological functioning.

"They are frequently, but not always, associated with various degrees of subjective distress and problems in social functioning and performance."

It develops in late adolescence and continues to be shown in adulthood.

Children under 16 are unlikely to show signs of personality disorder, says the WHO.

A personality disorder affects behaviour in a range of different settings and does not change. A diagnosis usually has to include at least three traits or behaviours which are deemed to be evidence of a disorder.

In the past, people from different cultures were committed to mental hospitals because their behaviour was deemed to be go against the norm.

The international guidelines recognise this and say personality functioning must take into account the individual's ethnic, cultural and social background.

Both the WHO and the APA group personality disorder in three broad categories, but they disagree on the labels within these.

The first includes paranoia and schizoid or schizotypal disorders.

The second includes antisocial behaviour, people who have an inability to control anger and suffer unpredictable mood swings and borderline cases such as people who resort to self harm.

The third embraces obsessive compulsive disorder-type traits and hyper-anxiety.

Antisocial behaviour

The Royal College of Psychiatrists says there is no "entirely satisfactory" diagnosis of antisocial traits which threaten public safety due to the complexity and range of cases.

It says diagnoses change and forensic psychiatrists "are often prisoners of their time".

Antisocial or severe personality disorder is generally taken to be behaviour which shows "a gross disparity between behaviour and prevailing social norms".

Doctors are undecided as to whether personality disorder can be treated.

According to the mental health charity SANE, 10% of psychiatrists believe severe personality disorder is untreatable.

Another 10% think it is treatable and the rest are undecided.

The Mental Health Act 1983 only allows people to be committed to hospital where psychiatrists believe the person is treatable.